diff --git a/src/buffer.c b/src/buffer.c
index bb9c773..27e8643 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4170,8 +4170,11 @@
     {
 	stl_items = ALLOC_MULT(stl_item_T, stl_items_len);
 	stl_groupitem = ALLOC_MULT(int, stl_items_len);
-	stl_hltab  = ALLOC_MULT(stl_hlrec_T, stl_items_len);
-	stl_tabtab = ALLOC_MULT(stl_hlrec_T, stl_items_len);
+
+	// Allocate one more, because the last element is used to indicate the
+	// end of the list.
+	stl_hltab  = ALLOC_MULT(stl_hlrec_T, stl_items_len + 1);
+	stl_tabtab = ALLOC_MULT(stl_hlrec_T, stl_items_len + 1);
     }
 
 #ifdef FEAT_EVAL
@@ -4251,11 +4254,13 @@
 	    if (new_groupitem == NULL)
 		break;
 	    stl_groupitem = new_groupitem;
-	    new_hlrec = vim_realloc(stl_hltab, sizeof(stl_hlrec_T) * new_len);
+	    new_hlrec = vim_realloc(stl_hltab,
+					  sizeof(stl_hlrec_T) * (new_len + 1));
 	    if (new_hlrec == NULL)
 		break;
 	    stl_hltab = new_hlrec;
-	    new_hlrec = vim_realloc(stl_tabtab, sizeof(stl_hlrec_T) * new_len);
+	    new_hlrec = vim_realloc(stl_tabtab,
+					  sizeof(stl_hlrec_T) * (new_len + 1));
 	    if (new_hlrec == NULL)
 		break;
 	    stl_tabtab = new_hlrec;
diff --git a/src/testdir/test_tabline.vim b/src/testdir/test_tabline.vim
index 5560a21..e58a412 100644
--- a/src/testdir/test_tabline.vim
+++ b/src/testdir/test_tabline.vim
@@ -134,6 +134,17 @@
   set tabline=
 endfunc
 
+" When there are exactly 20 tabline format items (the exact size of the
+" initial tabline items array), test that we don't write beyond the size
+" of the array.
+func Test_tabline_20_format_items_no_overrun()
+  set showtabline=2
 
+  let tabline = repeat('%#StatColorHi2#', 20)
+  let &tabline = tabline
+  redrawtabline
+
+  set showtabline& tabline&
+endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 5cb7218..eaf29a4 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4419,
+/**/
     4418,
 /**/
     4417,